Perspective Rules Illustrated

Additional Elementary Rules

A right line is a perfectly straight line in a position or direction. Parallel lines are lines which are the same distance from each other throughout their length, whether straight or curved.

A horizontal line is one which is parallel to the earth’s surface or the sea level.

A vertical line is a perfectly upright one, pointing to the vertex or
zenith and to the center of the earth.

A perpendicular line is a line at right angles to any other straight line, but is not necessarily vertical.

A plane is a perfectly level surface, which may be either horizontal,
vertical, or inclined in any direction.

A straight rod applied to any such surface would touch it throughout its length and breadth. A line is said to be in a certain plane when throughout its length it touches the plane, or coincides with it. In perspective, the picture plane is the surface, paper, canvas or whatever it may be upon which the drawing is made. This is always supposed to be at right angles to the direction in which the spectator is looking. If we are standing erect, and looking straight in front of us, the picture plane will be vertical; for instance, if the picture were placed close to an ordinary wall, the picture plane would be vertical. A point on the picture plane exactly opposite the eye is called the center of vision. The horizontal line indicates on the paper the position of the natural horizon. It will be higher or lower, according to the position of the spectator. If the latter stands on a hill, the horizon line would be high. If he stands on a level with the sea beach, the horizon line will be low.

The three principal methods of representing objects are orthographic, isometrical and perspective projection. Linear perspective is the only one with which we deal.

An Illustrated Summary

One may successfully copy a picture without a knowledge of perspective, just as a carpenter may, if he has plans before him, erect an intricately constructed building without a knowledge of architecture; but no man could properly prepare such plans without any acquaintance whatever with the rudiments of the laws of architecture. One cannot paint well without some knowledge of drawing. One cannot draw more than the simplest picture without some knowledge of perspective.

The horizon of perspective, the horizon line, is more readily understood if you will imagine yourself standing at the sea shore gazing out upon the water. Where the sky apparently meets the water, is the horizon. Seen in a picture, from the level of a low beach, the line appears low down, under the middle of the picture. Now, go upon some promontory, and the horizon seems to go up with you, and in a picture would appear above the middle of the picture.

Imagine a large number of high poles placed upright in the sea, each pole twenty feet above the water’s level, extending at right angles to the shore far out at sea. (Fig. 18.) Now, if the line of poles comes within the range of your vision, each one that is more distant from you than the other will, in turn, seem to get smaller and smaller until the last one seems to disappear, as in Fig. 18. Row out on the sea until the poles are at right angles with the line of vision and the poles will appear as in Fig. 19.

Now row back to shore. We will suppose that another line of posts has been placed at right angles to the first mentioned. Their arrangement is shown in the plane diagram in Fig. 20. If you stand a little to the left of the nearest pole they will appear as seen in Fig. 21.

We will now suppose that the second row of posts has been taken up again and transplanted parallel with the first row, but a hundred feet away. Stand half way between them, but crouch close to the ground, and they will appear as in Fig. 22. The horizon will seem to have been lowered with you. Now stand on an elevation and look again. The horizon will seem to have risen with you. (Fig. 23.) Return to the place where you first stood, a rod or so to the left, and gaze again; the poles will appear as in Fig. 24.

Note: The horizon line in each of the figures is indicated by an A.